In recent years, discontinuous reception (DRX) has been increasingly used as a function for saving power consumption for data transmission and reception between a base station device (eNB: evolved node B) and a mobile station device (UE: user equipment). The DRX is implemented in such a way that the power supply is turned on at a specific timing and is turned off when there is no data transmission and reception for a fixed time period.
An effect of power consumption saving may be improved by lengthening the off-time of the power supply in the DRX. However, when the power supply is turned off, data reception is disabled and thereby a communication delay may occur. Therefore, it is preferable to optimize DRX parameters determining the DRX setting such as an off-time of power supply in order to attain a proper balance between the power consumption saving and the communication environment.
DRX parameters affecting the off-time of the power supply in the DRX include, for example, a DRX cycle, an on-duration time, and an inactivity timer. The DRX cycle is a parameter indicating a length of an ON and OFF cycle of power supply. The on-duration time is a parameter indicating duration of monitoring data transmission and reception after the power supply is turned on. The inactivity timer is a parameter indicating an extension time of the monitoring duration, when data is transmitted or received.
A related technique of dynamically changing the DRX parameters responds to a change of the load by measuring only present load information in a single eNB, and changing the DRX parameters at a timing when the load difference exceeds a threshold value.
In recent years, there have been increasing small-size cells of base station devices along with an increase in use of smart phones and a resultant increase in data communication traffic. With the small-size cells, since each eNB covers a small area, a specific characteristic of users may be found out. That is, use tendency at each eNB has a close relationship with a time zone and an event which occurs in the covered area.
For example, as for an eNB located near a transport facility, the possibility of communication is considered to increase when a transportation disorder occurs, because people involved may try to know the cause of the transportation disorder and find out an alternative transportation route. This may results in an increase in communication to the eNB. Further, in recent years, push-type services for smart phones have been increasing. The push-type services include, for example, services for providing life information such as disaster alarm mail, road information, and weather information. Many of such push-type services start communication upon occurrence of an actual event such as a disaster. In other words, in the case where a push-type service is provided, a large volume of communication may occur in response to the occurred event. In this case, communication to the eNB may also be increased.
As a technique of implementing the discontinuous reception, there is a related technique that determines the discontinuous reception cycle on the basis of an incoming call history. There is another related technique that changes the discontinuous reception cycle on the basis of an incoming call frequency. There is yet another related technique that changes the discontinuous reception cycle upon occurrence of an outgoing call to an emergency telephone number.
Related techniques are disclosed in, for example, Japanese Laid-open Patent Publication No. 2010-288278, Japanese Laid-open Patent Publication No. 09-331288, Japanese Laid-open Patent Publication No. 05-183478, and International Publication Pamphlet No. WO2007/066393.
According to the related technique that changes the DRX parameters when a present load in a single eNB exceeds a threshold value, the DRX parameters are not changed until the load actually becomes high. For this reason, the DRX parameters are changed only after elapse of a certain period of time following the occurrence of an event which increases communication. This means that it is difficult to set appropriate intervals of the discontinuous reception in a case where communication traffic concentrates immediately after the occurrence of an event. If increase of communication is kept for a certain period of time after the occurrence of an event, an appropriate setting for the certain period of time may be assured by one-time measurement of the load. Instead, in the case where there is an irregular or regular increase in the communication traffic, it is preferable to increase the frequency of measuring the load in order to change the parameters at an appropriate timing. To this end, in the related technique, the eNB has to calculate a change difference frequently, and may have increased load.
Even with the related technique that changes the intervals of the discontinuous reception on the basis of the incoming call history or incoming call frequency, it is difficult to set appropriate discontinuous reception while keeping the load on a base station device low, since the technique does not consider an increase in the communication traffic due to the occurrence of a specific event. With the related technique that changes the intervals of the discontinuous reception at the timing of an outgoing call to an emergency telephone number, it is also difficult to set appropriate discontinuous reception while keeping the load on a base station device low, since the intervals of the discontinuous reception are not changed unless a specific state occurs.